The present invention relates generally to a superconductive magnet having a shock-resistant re-entrant tube suspension, and more particularly to such a magnet whose re-entrant tube suspension is also more resistant to buckling when subjected to a shock.
Superconducting magnets include superconductive coils which generate uniform and high strength magnetic fields. Superconducting magnets include, without limitation, those used in magnetic resonance imaging (MRI) systems employed in the field of medical diagnostics and those proposed for superconducting rotors and for superconducting energy storage systems. Known techniques for cooling a superconductive magnet include those in which the superconductive coil is cooled through solid conduction by a cryocooler coldhead and those in which the superconductive coil is immersed in a cryogenic fluid (e.g., liquid helium).
Known magnets include those in which the superconductive coil is surrounded with a spaced-apart thermal shield which is surrounded with a spaced-apart vacuum enclosure. Known suspension systems include re-entrant tube suspension systems which include fiberglass outer and inner support cylinders. It is noted that stiffening rings associated with cylinders are known in unrelated art areas such as on a five-gallon drum. The outer support cylinder: is located within and generally spaced apart from the vacuum enclosure; is positioned outside and generally spaced apart from the thermal shield, has a first end rigidly connected to the vacuum enclosure, and has a second end rigidly connected to the thermal shield. The inner support cylinder: is located within and generally spaced apart from the thermal shield, is positioned outside and generally spaced apart from the superconductive coil, has a first end rigidly connected to the thermal shield near the second end of the outer support cylinder, and has a second end located longitudinally between the first and second ends of the outer support cylinder and rigidly connected to the superconductive coil.
The fiberglass outer and inner support cylinders provide low thermal loss and provide some protection against shock and vibration forces. For example, an MRI magnet is susceptible to shock and vibration forces during shipping and installation, and a naval magnet is susceptible to shock and vibration forces while in use during mine-sweeping operations. Shock and vibration forces during shipping and installation subject the superconductive coil to deflections within the vacuum enclosure leading to frictional heating at the magnet's suspension points which can prevent superconductive operation, as can be appreciated by those skilled in the art. Likewise, shock and vibration forces during magnet operation subject the superconductive coil to deflections within the vacuum enclosure leading to frictional heating at the magnet's suspension points which can cause the magnet to quench (i.e., lose its superconductivity). Although the re-entrant tube suspension system provides some protection against such shock and vibration forces, it has a tendency to buckle under large loads (such as, without limitation, axially-compressive, radially compressive, transverse, and/or torsional loads). What is needed is a superconductive magnet having a re-entrant tube suspension with improved resistance to buckling.